Yes, we do have some general rules in terms of the number of trees needed for a fire history study using tree rings. For each site, we tend to want at least 10-15 trees. However, there is some wiggle room there since it depends on whether the trees we sample have picked up on a lot of fire activity or not. Some trees are better than others at documenting the fires that occur around their bases. In some studies, I’ve seen 20-40 trees included per site.